Start printing pcb stencils for about $200

I don't like waiting for stencils or messing around with chemicals, so I recently bought a Silhouette Portrait cutting plotter in hopes that I could cut my own. It can also cut other things like vinyl decals. Current prices for the cutter and a pack of transparencies on Amazon come to about $200. I cut a few test stencils, and the results look pretty usable for the SOT-23 and 0603 footprints in my test file. Better than laser cut, at least for mylar and the lasers I've used.

Stencil cut on a Silhouette Portrait.

When I pulled it out of the box, apart from a sudden overpowering urge to get a tiny dog, name it Precious and start sending hand crafted greeting cards to all my friends, all I really noticed was how unassuming it looked. It's actually a lot like a regular cheap-o printer. The only real difference is there is a sticky mat for materials that don't have a backing (the pale blue sheet is the mat), and it has a blade instead of an ink cartridge.

Silhouette Portrait.

How to make stencils:

Windows:

If you're on Windows you'll probably have good success following Cathy Saxton's instructions here: http://www.idleloop.com/robotics/cutter/. Scroll down to "Cutting Mylar for Solder Stencils" at the bottom. The instructions are for the Silhouette Cameo, but they worked for me on the Portrait. Be sure to turn off scale-to-fit on DXF import or your stencil won't be the right size.

Linux:

There is a program called Robocut which I updated to control the Portrait. I have run it successfully, but no promises is won't make your plotter do things you didn't intend. To install:

sudo apt-get install libqt4-dev libusb-1.0-0-dev git-coregit clone git://github.com/nosliwneb/robocut.gitcd robocutqmakemakeadduser $USER lp(Now log out and log back in. If you don't want to log out you can run it as root immediately)./robocut

Creating the stencil file (Linux):

In your pcb editor, generate gerbers for the stencil.

Open the paste layer (.GTP, .GBP if you used Eagle) in Gerbv, and export as .SVG.

Open the .svg file in Inkscape. I haven't spent any time tracking down why this is necessary, but you'll probably need to scale everything to 125%, at least I do. Crtl-A, then Object... Transform... Scale. Position it where you want on the page, and draw the stencil edges by placing a rectangle over everything. If there are board edges in your file you'll want to delete them. Save.

Cut the stencil (Linux):

Open the .svg file in Robocut, start the cut dialog from the file menu, or Ctrl-P, and enter these settings:Media: Vinyl StickerSpeed: 1Pressure: 33

Conclusion:

I'm using 0.004" material. There have been some issues with corners not wanting to release, moreso on Linux. I haven't experimented too much with the settings, so improvements may be possible. I did run one set of stencils twice in a row, and the second cut registered right on top of the first. That one released much better, but still not perfect. I had fewer release issues on the stencil I cut with Silhouette Studio in Windows, so I'll probably just use that from now on.

After reading a little more on the subject, it looks like this plotter uses a proprietary control language called GPGL, as opposed to the standard HPGL that most commercial plotters understand. I think if I had it to do over, I'd probably buy something like the USCutter MH series. That way I could use any of a variety of control programs, Windows or Linux, and the replacement blades aren't sold at HP print cartridge level prices. But I'm still happy with the Portrait, though. I won't need it that often and it should be just fine for the things I want it to do.

If you're feeling adventurous, you might also give Peter Monta's gerber2graphtec a try: http://pmonta.com/blog/2012/12/25/smt-stencil-cutting/. I didn't test it, but he claims you can get usable results down to 0201. I suspect you'll need to modify it to add the USB vid, and maybe other edits before it will work with the Portrait.

If you ever find yourself with an unsupported Silhouette plotter, running the following unix command after plugging it in should give you it's USB product id:

dmesg|grep "vid 0x0B4D"

Then search for "PRODUCT_ID" in Plotter.cpp in the robocut project and make the appropriate additions (2 places). Note that this may not work if Silhouette changes the command language for the new plotter.

A word of warning; Ubuntu uses an old rev of gerbv, and that version (2.5) has a bug that "Fix a bug where very thin flashed rectangles in logos/images from Eagle CAD were not always rendered." so QFP leads pads were a problem. I found this out the hard way.

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Vivien
2 years, 4 months ago

Hello,Great article, pcb stencils are sooo expensive.Do you think it could work for 0402 ?How much cost a mylar sheet ?Instead of writing "adduser <you> lp" it would be better to write "adduser $USER lp", no ?